Organotin compounds are known for their high degree of activity against microorganisms, such as fungi, bacteria and algae, and against insects, mites, molluscs and other small living beings.
It is of special significance that these compounds differ from other biocides, which contain heavy metals, such as copper or mercury, in organic or inorganic compounds, in that the tin compounds decompose to nontoxic inorganic tin compounds by physical, chemical and biochemical processes.
Another advantage afforded by the organotin compounds is their activity against pests which may be resistant to conventional biocides.
German Pat. No. 950,970 discloses for the control of microorganisms, such as fungi, bacteria and Protozoa, a pesticide containing an active ingredient consisting of an organotin compound of the formula EQU R.sub.3 SnX,
wherein R represents is an organic moiety and R.sub.3 represents three such moieties which may be the same or different.
It is apparent from the specification that R can be methyl, ethyl, propyl, butyl or phenyl. In the formula R.sub.3 SnX, X can represent OH, O-acyl, O-alkyl, SH, S-alkyl, S-aryl, SO.sub.2 -alkyl, SO.sub.2 -aryl, NHSO.sub.2 -alkyl or NHSO.sub.2 -aryl. The respective alkyl and aryl groups may be substituted or unsubstituted. The document does not, however, contain any information regarding the nature of the triorganotin compounds in case an alkyl residue or aryl residue is linked by a sulfur atom to the tin atom.
It is also known to change the toxicity profile by a controlled selection of the organic groups attached to the tin atom. For instance, the replacement of butyl groups by cyclohexyl groups results in tricylohexyltin compounds which are highly effective and hardly detrimental to plants. It is known that tricyclohexyltin hydroxide (Cyhexatin) (Laid-open German Application No. 15 42 863) and tricyclohexyltin triazole (AZO-cyclotin) have a prolonged nonsystemic activity against mobile spider mite stages, even against pesticide-resistant species.
By the attachment of suitable biocidal groups to the fourth valency bond of the tin atom of these tricyclohexyl tin compounds the latter can be converted to compounds having a synergistically improved activity. For instance, Laid-open German Application No. 15 42 863 describes arachnicides which contain tricyclohexyl tin compounds in which the fourth valency bond of the tin atom is saturated by an alkyl or alkylene residue, such as lauryl tricyclohexyltin or oleyl tricyclohexyltin. An attachment to the molecule may be effected via a sulfur atom which has a free valency bond that is saturated by an alkanoyl residue or benzoyl residue, such as lauroyl thiotricyclohexyltin. An attachment of a thioalkyl or thioalkylene residue to the fourth residual valency bond of the tin atom is not apparent from that document.
The biological activity of all these compounds is inadequate for the control of certain pests, particularly of mites.
In accordance with a proposal disclosed in Laid-open German Application No. 20 59 279, sulfur-containing trihexyltin compounds in which the sulfur atom is attached to tin and to a lower alkyl group are described, inter alia. That printed publication does not teach the use of a lower alkyl group other than the propyl group.
Whereas the previously known organotin compounds are useful insecticides, they have only a restricted field of application because they result in phytotoxic damage to numerous plants.